Abstract : The frequency-wave-vector dispersion relation for lattice waves traveling in several symmetric directions of tantalum has been measured at 296 K, using methods of neutron inelastic scattering. The results show strong similarities with the previously measured values for niobium. The results can be fitted by a Born-von Karman force model only if very long-range forces are invoked. Because of the peculiar nature of the relation, the Debye approximation appears to be better for tantalum than for most other materials. (Author)